1. Technical Field
This invention relates generally to the fields of Radio Frequency (RF) mixers and oscillators. More particularly, the invention relates to the integration of mixers and oscillators.
2. Description of the Related Art
Oscillators are used to provide a time varying signal in electronic circuits and are well known to those of skill in the art. FIG. 1 illustrates a typical oscillator known in the art. This oscillator is a negative resistance cell 10. A simple differential pair of transistors Q1 and Q2 is shown. The emitters of both devices, e1 and e2, are connected, either by a short circuit or other connection, thereby defining a common node n1. Current source I1 is connected to the common node n1. In the most basic case the current source I1 is a direct current (DC) source, as shown.
CN1 and CN2 are symmetric coupling networks, which may consist of short circuits, capacitors, transistors, or other circuit elements alone or in combination. For instance, if CN1 is an RC network, then CN2 is preferably an identical RC network. Connecting coupling networks CN1 between b1 and c2, and CN2 between b2 and c1, as shown, generates a differential negative resistance between nodes a and a′, or between any other two symmetric differential points in circuit 10 such as between bases b1 and b2, or even between corresponding differential points inside networks CN1 and CN2. For instance, if CN1 has a first resistor, then by symmetry CN2 preferably has a corresponding second resistor, and a differential negative resistance can be found between one node of the first resistor in CN1 and another corresponding symmetric node of the second resistor in CN2.
If a connection is made between a and a′, such that the connection provides an impedance with a real component greater than or equal to the real value of the negative resistance, circuit 10 will oscillate. The frequency of the oscillation will be determined by the impedance connected between a and a′. The oscillating output signal is produced over the connection between a and a′. In frequency conversion applications, the desired output signal is typically used as a signal source for another circuit.
FIG. 2 illustrates a single balanced mixer 20, which is known in the art. A differential pair of transistors Q3 and Q4 is shown. The emitters e3 and e4 are connected in the same manner as those in FIG. 1, thereby defining common node n7. A current source I2 is connected to the common node n7. In this instance, the current source I2 has both a DC component (Idc) and a frequency component (IRF) at frequency fRF.
Unlike the negative resistance cell 10, there is no cross coupling. Instead a frequency source, S1, providing an LO (Local Oscillator) signal at frequency fLO, is connected between bases b3 and b4. This LO signal varies the amount of current flowing through each transistor Q3 and Q4 such that the differential component of the current, provided by collectors c3 and c4 when a load is connected between nodes d and d′, has frequency components at DC, fLO, and fLO±fRF. In frequency conversion applications, the desired output signal is typically one of the frequency translated components of IRF, at either fLO−fRF (down-converter) or fLO+fRF (up-converter).
Although known oscillators and mixers can be combined, as they are in frequency conversion applications, the result is often far from ideal. In most applications, the mixer and oscillator are separate circuits. This results in an increase in both component area and power consumption, which results in a device that is costly to manufacture and operate. Furthermore, the physical distance between oscillator and mixer circuits often results in leakage of the local oscillator signal to other circuits, which is disadvantageous, as one of skill in the art will appreciate.
It is, therefore, desirable to provide a device that provides the functionality of both an oscillator and a mixer, which decreases the required power and area required to implement. Additionally, it would be desirable to provide a device that reduces the leakage of the oscillator signal to other circuits.